In recent years, there have been cases where a plurality of batteries are connected in parallel as a battery device mounted on vehicles such as electric forklift trucks, hybrid automobiles, electric automobiles, etc. in order to supply a large amount of electricity to the load in a stable manner.
Also, there is a battery monitoring device, for monitoring the state of each of such batteries, that is provided with a control unit for permitting the charging/discharging of each battery in accordance with the monitoring result of each battery. In these battery monitoring devices, identification information has to be set for each monitoring unit in order to transmit monitoring results from a plurality of monitoring units to the control unit, the monitoring units being for monitoring the states of the batteries.
As a related technique, there is a technique in which when for example respective monitoring units and the control unit are connected in series, each of the monitoring units adds, to a packet to be transmitted from a previous monitoring unit, information representing whether or not the identification information is set to itself so as to transmit it to a subsequent monitoring unit and the control unit sets identification information for a monitoring unit which is identified by the information added to a packet transmitted from the last monitoring unit and for which identification information is not set (Patent Document 1 for example).
Patent Document 1: Japanese Laid-open Patent Publication No. 2001-203733